RELATING TO THK ERI PTIX i: HIKX<>MENA OF
MONTE SOMMA, YEsrvirs
AND VOLCANIC ACTION IV GENERAL.
H. J.'JOHMSTOX-LAVIS Esqr., M.D., M.R.C.S., B. is Sc., F. G. S., etc.
L I S T
Books, memoirs, principal Ititterf ;;</, otlh'r signed publications of the author
1876 TO 189O
PRINTED BY KERRANTE, VICO TIRATOIO
Itt. QETTY CENTER
RELATING TO THE ERUPTIVE PHENOMENA OF MONTE SOMMA,
VESUVIUS AND VOLCANIC ACTION IN GENERAL.
H. J. JOHNSTOX-LAVJS Esqr. M. D., M. R. C. S., B. 6s Sc., F. G. S., etc.
111 the years from 1879 to 1883 much attention was devoted by
me to the elucidation of the geological history and physical phenome-
na as illustrated Ivr the products of the great Neapolitan volcano. In
the spring of 1883 the results of my investigations were embodied
in a long memoir which was forwarded to the Geological Society of
London, where it was read on June 20 th 1883. ( Abstracts of the Pro-
ceedings of the Geol. Soc. London. Session 1882-83 ) p. 100 and in
part published in February 1884. Unfortunately much of Part I. re-
ferring to the origin of the mountain was excised as well as HO con-
clusions, at the end of my memoir, to which I had been led by my-
researches. This has exposed me to two inconveniences. In the first
place I have been violently attacked regarding my explanation of the
form of the Somma- Vesuvius massif which could hardly have oc-
curred, or at least that part which refers to the question of when
and how the Atrio crater was excavated , had the entire memoir
appeared. In the next place other writers at much later dates have
brougt forward deductions similar to my own. To prevent further
trouble I have now published the conclusions which I hope will serve
as a guide to vulcanologists in other regions.
Many of those conclusions have been extended and published
in another paper (The Relationship of the Structure of Rocks to the
Conditions of their Formation.) Scicntif. Proceed. R. Dublin Soc.
Vol.V., N.S., July 1880, pp. 113 to 150) which was first offered to
the Geol. Soc. of London, read, but refused publication (The Phy-
sycal Conditions Involved in the Injection, Extrusion and Cooling
of Igneous Matter. ( Abstracts of the Proceedings of the Geol. Soc.
Lond. Session 1884-5. p. 78). As unfortunately many investigators
who occupy themselves with this question are unacquainted with
that paper, the conclusions that led up to its elaboration can now
be in their hands.
CONCLUSIONS AND DEDUCTIONS
1. Monte Somma is comparatively late as a volcanic focus in the
Campi Phlcgrsei , to which it belongs.
2. This is proved by the absence of leucitic rocks in the volcanic
tufa upon which it rests.
.?. There is no distinct evidence to prove that these latter igneous
products issued by the same vent that gave birth to Mt. Som-
ma. They were probably the result of submarine or sub-aerial
eruptions in the same volcanic area.
4. That the volcanic tufas earlier than Somma repose on late tertiary
marls etc. , of non volcanic origin, these again on the eocene
" Mac iff no" which in turn mantles the cretaceous appeuine
5. Judging from what we know of the first appearance of all new
volcanoes, like them, this one commenced by an explosive
6. That this first eruption gave rise to pumiceous ejectamenta similar
to products that were formed in its later intermittent stages.
7. This eruption has passed by gradation into a state of chronic
activity such as we see portrayed in the leucitic lavas in the
escarpment of the A trio.
8. This chronic activity was the great agent in building up the main
bulk of the mountain, and the phenomena were very similar
if not identical with those from A. I). 1031 to the present
day going on from the Yesuvian cone.
9. From arrest of supply of magma or exhaustion of heat in the
volcanic canal, the igneous forces failed for the time being to
make themselves shown at the surface, but were probably
storing up energy for a future outburst so producing an appa-
rent extinction of the volcano.
10. This apparent extinction was broken from time to time by
11. These eruptions were due to the contact of superheated igneous
matter with water-bearing rocks , during which they ab-
sorbed a certain amount of aqueous matter proportioned to
the temperature, pressure and length of contact. In this man-
ner the eruption would take place when the elastic tension
of the volatile constituent of the magma overcame the super-
IS. This eruption might be hastened or determined by increased
pressure coming from below at the igneous reservoir or source
of igneous matter.
13. The products of such an eruption must have a tendency to be
fragmentary and vesicular in proportion to the temperature
and amount of igneous matter in the magma.
14. That vesicular structure is due to the molecular conversion of
the dissolved or combined aqueous matter into vapour. This
change resulting in the absorbtion of much heat, so as to
cause the rock mass to solidify before the vesicles could escape.
15. In rocks that have reached the surface, crystalline structure or
the proportion of formed matter that separates after ex-
trusion depends also upon the rapidity of cooling which is
seen to be chiefly due to the amount of included volatile matter.
16. That when this volatile matter is small in quantity, instead of
the igneous magma being torn assimder by its own inherent
expansion, il will issue as a continuous stream forming a lava
flow , which will possess a high temperature relatively to
what itroriginally had, less what would be lost by the expansion
and escape of aqueous vapour.
17. Cooling will be proportional to the last cause and to the rapi-
dity and viscisitudes of outflow.
18. That as extratelluric crystallisation of a pumice is in a ratio to
its rapidity of cooling, so also is that of lava.
19. This explains the fact observed at Vesuvius and elsewhere that
lava of fine grain contained much water and vice versa.
20. The most favourable circumstance to complete large consti-
tuent extratelluric-formed crystals are 1 st primitive high tem-
perature of the igneous matter, 2 nd the small loss of heat from
the paucity and therefore volatilization and escape of vapour,
3 rd the length of time the fluid magma is retained simmering
under low pressure in the chimney of a volcano.
21. That this also explains why the very small streams that gutter
over the edge of the vesuvian crater arc rich in large leucites
and pyroxenes as all those produced by the almost continuous
outpour of lava during the last ten years, but are absent from
long streams such as the fine examples of 1872 and IftU.
??. That there is a distinction between pumice and scoria.
?:i. This difference depends upon the origin and character of their
respective vesicular structure. In the case of pumice, the ca-
vities result from the interstitial molecular separation and
union of a gaseous or volatile matter, which in part escapes
breaking up and carrying with it the fragments of the igneous
rock which from their consequent rapid cooling prevent the
escape of the residual vapour bubbles resulting in the spongy
structure. In scoria the vesicularity is due to the formation
of a froth, the cavities being formed not solely from the local
inherent volatile matter alone, but from that derived from
all the thickness of a mass of lava, which floats to the top to
form a scum.
As the vapour will only rise through the pasty mass when
the bubbles are of considerable size, the cavities in scoria
arc proportionally large in comparison to those in pumice.
As the mass-weight of a vesicular rock is dependent upon
the cubic area of the vesicles, other things being alike this
accounts for a pumice weighing less, bulk for bulk, than the
The higher Sp. G. of the crystalline components of the scoria
also and the abundant vitreous matter composiifg the base of
the pumice will make a still greater difference between them.
24. That not only does igneous matter modify the rock walls in
which it is contained, but that they also may modify its com-
position bj* an interchange of chemical constituents.
25. That in an eruption the ejectameuta is made up of three ele-
Primary or essential. The true igneous matter in the form
of lava, pumice, scoria, ash etc. Secondary or accessory:
Materials derived from the crater walls of the cone i. e.
cooled rocks and othe*r products of earlier eruptions derived
from the same volcano. Tertiary or accidental: Rocks
which compose the basis of a volcano; and which may be
igneous, or sedimentary rocks derived from other sources. (1)
( ) Perhaps the second of each of these terms is more suitable, so
avoiding any confusion of the yreat divisions of sedimentary rocks.
26. A very high temperature and much aqueous matter produce*
a vitreous pumice.
: J 7. A very high temperature ami less aqueous matter produces a
?8. A high temperature and little aqueous matter produces a pu-
miceous scoria rich in large crystals, hut with a vitreous base
(within certain limits).
29. The two latter conditions hut especially the last seems most
i'avourable to the crystallization of Leucite.
:t(t. That it may be stated generally that Amphibole and Sanidine and
other felspars are commonest as minerals formed previous to
escape of explosive ejectamenta, (intratclluric) whereas Augite
and Leucite belong to the ejection ami subsequent period and
are commononest in non explosive lavas etc.
'II. That the pumice was not derived from the tearing up of earlier
trachytic rocks beneath M te Somina (Scrope) but were in each,
independaut productions from the heated matter producing
the eruption. If they were not so, we should expect each de-
posit to he a mixture of different kinds of pumice , whereas
by a single hand specimen the eruption can be determined by
which it was ejected.
.?. M 4 c Somma was originally a pretty regular cone, about 7000
feet or 2300 meters high.
.9.9. Each explosive eruption hollowed out or enlarged the size of
the crater up to a certain limit.
>4. Either the first or some later explosive eruption did not occur
from the original axis of the mountain, but from a point slight-
ly to the west of south of it.
:t.~>. The later of these eruptions enlarged the crater to such an
extent as to carry its apex below drainage level, thus modi-
fying the eruptive phenomena.
36. This crater extended below the base of the mountain through
the tertiary rocks into the Appenine limestone.
::i . These rocks especially the latter were highly metamorphosed
by previous contact with igneous matter, thus accounting for
the great variety of ejected blocks.
9tf. That barancos produced by either one or two methods or both
combined, opened into the crateral hollow and drained it.
.9.9. The result of such drainage was the local deposit of a breccia
Phase III, period 4, on the slopes or foot of the mountain
near that locality now seen in the Vallone <iraude and its
neighbour Valloue di Pollena.
In. That Lyell's statement that there were valleys of denudation
between one tafa and another is perfectly correct.
//. These valleys do not necessarily correspond to the recent ones,
but that probably little alteration has occurred in the basin
drained by each.
-12. The eruption that commenced as a violent explosive one pro-
ducing a very vitreous pumice by a series of probably inter-
mittent stages, terminated by the outflow of true lavas.
43. The products of the first outburst of an explosive eruption arc
much more vitreous and poorer in formed matter than that
ejected later , in which the expansive force has deminished.
This is the result of the longer time allowed for cooling by
that portion which is deepest in the volcanic chimney and
which also from being enclosed in dryer rocks had probably
absorbed less water.
44. The present chronic activity was the. gradual result of a series
of eruptions begining as an explosive one similar to that of
the year A. D. 79.
4o. The vesuvian cone is not concentric with the old M te Somina,
but it is roughly with that of the axis of the eruptions that
formed the great crater of the Atrio del Cavallo.
46. The valleys present different and special characters in different
parts of their course which depend upon the change in the
angle of inclination, and upon the kind of rocks traversed.
47. That the phenomena of the prehistoric volcano were- similar in
all respects to what we know as occuriug in historic times.
48. Volcanic action depends first upon variations of tension in the
primary igneous mass, and this is modified in violence and
the character of its products, by the different conditions to
which the escaping portion is subjected in reaching the sur-
face and its deposition there.
49. In all probability the volcanic products of the neigbourhood are
all derived from the same reservoir as that of Vesuvius, but
difference in composition and structure is due to the various
influences brought to bear on the original primitive matter in
its journey from its source, to its deposition upon the surface.
~)(). That nearly all the superficial manifestations of volcanic action
can be explained without exception by this theory originating in
the study of, and illustrated by, Monte Somma and Vesuvius.
LIST OF BOOKS, MEMOIRS, PRINCIPAL LETTERS AND OTHER
PUBLICATIONS OF THE AUTHOR FROM 1876 TO 1890
/ 1870. On the Triassie Strata which arc Exposed in the Clifi-
sections near Sidmouth, and a Note on the Occurrence
of an Ossiferous Zone containing Bones of a Labyrintho-
don. Quart. Journ. Geol. Soc. Loud. Vol. XXXII, pp.
274 to 277, with 2 woodcuts & i plate.
2 1877. Notes on the Geology of Lewisham: Proceed. Geof.
Assoc. Lond. Vol. IV, pp. 528 to 543, with 5 woodcuts.
3 1878. A Glass-eating Lichen. " Science Gossip" N. 162.
June, pp. 128-130, with 4 woodcuts.
I 1879. A short History of the Town of Stalbridge, Staplebridge,
Stawbridge , or Stapleford , Dorsetshire. Stalltridye
Alnmnach (Header's ) for 1879, pp, 1 to 3.
-5 1880. A Visit to Vesuvius During an Eruption. "Science
Gossip." N. 181, January, pp. 9 to 10.
f> 1880. Volcanic Cones , their Structure and Mode of Forma-
tion. "Science Gossip." N. 190, Oct., pp. 220 to 223,
with 1 woodcut.
7 1881. On the Origin and Structure of Volcanic Cones.
"Science Gossip" N. 193, Jan. pp. 12 to 14 , with 4
8 1880. Iron and Hydrogen. : "Nature," Vol XX H. p. 22O.
9 1880. Hardening of Steel. Ibid., p. 511.
10 1880. Note on the Comparative Specific Gravities of Molten
and Selidifed Vesuvian Lavas. Quart. Journ. Geol. Soc.
Lond. Vol. XXXVIII, p. 240 to 241.
11 1881. The Earthquake in Ischia. " Nature," Vol. XX HI,
12 1882. Diary of Vesuvius from Jan. 1 s * to July 10 th 1882. -
"Nature" XX IV, pp. 455 to 456 with 2 woodcuts.
13 1883. Earthquake in Naples. "Nature" Vol. XXVI, p. 151.
14 1883. Notice of the Earthquake of Ischia of March 4 th 1881.
Reports Brit. Assoc. Advancement of Science 1883.
15 1883. Notice of the Earthquake of Ischia of July 28 th 1883.
16 1883. The Disaster in Ischia. -- "Nature." Vol. XXV 111,
pp. 346 to 347.
17 1883. Observations scientiiiques sur le tremblement de terre
dii 28 Juillet 1888 a 1' isle d'Isohia. "IS Itnlif" \l}tn,n>\
August 13 1883.
18 1883. II parere d' uno scienziato. 77 Piccolo" f.\(tirfcx/
Sept. 2^ 1883.
l<) 1883. Previsions tic futures catastrophes dans Tile d'lschia.
" U Italie" (Rome) Sept, 2 nd 1883.
2() 1883. The Disaster in Ischia. " Indianapolis Journal."
Sept. 6* 1883.
21 1883. Una risposta al Prof. Pahnieri. "77 Piccolo" (Nfip/cs\
Sept. 8th 1883.
22 1883. Kturte sur 1' emplacement des nouvelles villes a 1'ilc
d'lschia. " U Italic" (Rome) Sept. 15* 1883.
23 1883. Le costruzioni a Oasamieciola. "// Piccolo" (Najifcs,
Sept. SO" 1 1883.
21 1883. Rapport preliininaire sur le tremblenient de terre dit
28 Juillot 1883 a 1' ilo d'lschia. " L' Tfftfir."' Sept. 22 lul
25 1883. The Ischian Earthquake of July 28th 188:*. -- " Nn-
fure," Vol. A' A' nil, pp. 437 to 439, with a map.
*0 1883. Notices on the Earthquakes of Ischia of 1881 and 1883.
with a Map of the Isoseismals. In 8., pp. 56. with 1 map.
21 1884. The Remarkable Sunsets. "AW>v," Vol. XXIX.
28 1884. The Late Eruption of Vesuvius. Ibid., p. 29 L
29 1884. The Geology of Monte Soinma and Vesuvius, being a
Study in Vnlcauology. Quart. Jonrn. Oeol. Soc. Loml..
Vol. XL, pp. 35 to 112. tritli 2 icoodcnts anrt I n'0i<>-
30 1884. Volcanoes on the Shore of Lake Nyassa, Africa. -
"Nature," Vol. XXX, pp. 62 to 63.
31 1881. Earthquakes and Seismographs. " Na'irrc" Vol. XXX .
pp. 608 to 612 with 5 icoodcuts.
32 1884. Brevi considerazioni intorno alia relazione del profes-
sorc L. Pahnieri sul tcrremoto dell' Isola d'lschia. " //
Piccolo" (Naples) Man-It 31 st and April pt 1884.
33 1885. Meteorite o Ciottolo? " It Piccolo" and "II Pm>-
f/olo" (Naples) Dec. 8i and 9 th ., "Roma," " Corr ;<>,-<>
del Mattino" (Naples) and " L' Italie" (Rome) Dec. W*,
"Piccolo, " "Pmu/olo" (Naples) Dec. 9 th and 10 th ..
(Naples) mid " L'KfW (Rome) of Dec. 10''.
" L' If 'alie " (Rome) Dec. 12*, " The Times" (London)
34 1885. The Physical Conditions Involved in the Injection,
Extrusion and Cooling of Igneous Matter Quart. Journ.
Geol. Soc. Loud. Vol. XL I, pp. 103 (o 106.
35 1885. Monograph of the Earthquakes of Ischia , a Memoir
Dealing with the Seismic Disturbances in that Island from
Remotest Times with Special Observations on those of
1881 and 1883 Lui.au, London ami Furchheim, Naples,
1885 in royal 4, pp. X and 112, with 20 photo-engrav-
ings, 2 large maps in color, 3 lithographic plates and
/ chromo-litliographic plate.
36 1885. The New Outburst of LaA~a from Vesuvius. "Nature",
Vol. XXII, pp. 55 and 108.
37 1885. First Report of the Committee for the Investigation
of the Volcanic Phenomena of Vesuvius and its Neigh-
bourhood, Jlrff. Assoe. Reports, pp. 2,
38 1885. On the Preparation of Sections of Pumice-stone and
other Vesicular Rocks. Journ. R. Microscop. Soc., Set.
II. TV. 17 puff. 32-31.
39 1880. Sounding a Crater, Fusion Points, Pyrometers, and
Seismometers "Nature" Vol. XXXV, p. 197.
lo 1880. The Relationship of the Structure of Igneous Rocks
to the Conditions of their formation Sclent if. Proceed.
R. Lublin Soc. Vol.V, 'N.S., pp. 112-156.
H 1880. On the Fragmentary Ejectamenta of Volcanoes Pro-
ceed. Geol. Assoc. Vol. IX, pp. 421 to 432 with 3 fig,
12 1880. Krakatao, "Nature" Vol. XXXIII, p. 6.
13 1880. Vcsuvian Eruption of February 4 th 1880 , Ibid.
14 1880. Notes on Vesuvius from February 4 th to August 7 th
1880. Md. p. 557.
15 1880. The Eruption in New Zealand. Geol. Mag., Vol. HI,
Dsc. Ill, pp. 523-521.
If) 1880. The Relationship of the Activity of Vesuvius to Cer-
tain Meteorological and Astronomical Phenomena. Pro-
ceed. Royal. Soc. Lond. N. 243. p. 1.
17 1880. Second Report of the Committee for the Investigation
of the Volcanic Phenomena of Vesuvius and its Neigh-
bourhood. Brit. Assoc. Reports, pp. 3, also "Nature''
Vol. XXXIV, p. 481.
48 1887. L'Eruzioue del Vcsuvio ncl 2 Maggio 1885. Ann.
ft. Accad. 0. Costa d. Aspirant i Naturalisti. Era 3. Vol.
1, Naples, pp. 8 with 1 photo-engraving and i cromo-
19 IS87. Diario del t'ciioiiicui avvenuti al Vcsuvio da Luglio 1882
ad Agosto 1880. "Lo Spettatorc del Vesuvio e del C(imi>i
Flegrei." 1 Nuova serie pubbltcata a cura ea spese delict
Sezione Napoletana del Club Afpinv Ifaliano. Fiirchheiin
Napoli 1887 in 4., pp. 81 to 103 with 13 photo-en-
30 1887. ( With Dr. G. C. V. Vosmacr ) On Cutting Sections
of Sponges and other Similar Structures with Soft and
Hard Tissues. Journ. R. Microscop. Soc. 1887, Part
2, pp. 200-205 with 1 woodcut.
51 1887. The Islands of Vulcano and Sfcromboli. "Nature" Vol.
XXXVI, pp. 13-14.
52 1887. Third Report of the Committee Appointed for the In-
vestigation of the Volcanic Phenomena of Vesuvius and
its Neighbourhood. Brit. Assoc. Reports 1887, pp. 3.
53 1888. On the Form of Vesuvius and Monte Somma. Geol.
Mag., Dec. Ill, Vol. V, pp. 443-451 with 1 woodcut.
54 1888. The Conservation of Heat in Volcanic Chimneys.
Brit. Assoc. Reports 1888, pp. '2.
55 1888. The Occurrence of Leucite at Etna Ibid.
56 1888. Not^ on a Mass Containing Metallic Iron Found on
Vesuvius IMd. pp. 2.
57 1888 Note on the Occurrence of Celestite Containing nearly
Fourteen per cent of Free Sulphur. Min. Mag. 1888,
58 1888. ( With Dr. T. Anderson ) Notes on the Recent Vol-
canic Irruption in the Island of Vulcano. Ibid, pp. 3.
59 1888. Fourth Report of the Committee for the Investigation
of the Volcanic Phenomena of Vesuvius and its Neigh-
bourhood. Ibid, pp, 7.
fj(J 1888. The Ejected Blocks of Monte Somma. Part I. Stratified
Limestones. Quart. Journ. Geol. Soc., Vol. XL IV
fjl 1889. Further Notes on the Late Eruption of Vulcano Is-
land. "Nature," Vol. XXXIX, pp. 1O9-H1.
62 1889. The Recent Eruption at Vulcano. Ibid. p. 173.
63 1889. The Recent Activity of Vesuvius. Ibid. p. 184.
64 1889. The State of Vesuvius. Ibid, pp. 302-303.
f>5 1889. The Present State of Seismology in Italy. Ibid,
66 1889. Su una roccia contenciite leucitc trovata siill'Etna.
Boll. d. Soc. d. Microscopisti It., Vol. I. Fasc. 1-2, pp.
26, with one photo-engraving.
67 1889. On a Remarkable Sodalite Trachyte Lately Discovered
in Naples, Italy. Geol. Mag., Dec. III., Vol. VI., N.2,
68 1889. L' Etat Actuel du Vcsuve. Bull. Soc. Beige de Geo-
logic, Hydrologie ef Paleontol., Vol. Ill, pp. 1-11 with 3
69 1889. II Pozzo Artesiano di Ponticelli. Rend. d. R. Ac-
cad, d. Sc. Fis. e Mat. d. Napoli., Giugno 1889, pp. 7.
70 1889. Volcans et tremblements dc terre. A review of what
lias been published on these subjets during the year 1888.
U Annuaire Geologique Universe!. Paris 1889, Vol. V.
71 1889. The New Eruption of Vesuvius. "Nature" Vol. XL.
72 1889. The Ponza Islands. -- Geol. Mag., Dec. Ill, Vol. VI,
pp. 529-535 with 3 woodcuts.
73 1889. Viaggio scientifico alle regioni vulcaniche italianc nella
ricorrenza pel centinario del Yiaggio alle due Sicilic
di Lazzaro Spallanzani. ( This is the programme of the
excursion of the cnglish geologists that visited the south
Italian volcanoes under the direction of the author. It is
here included as it contains various new and unpublished
observations ). Naples 1889 in 8., pp. 1-10
74 1889. Fifth Report Appointed for the Investigation of the Vol-
canic Phenomena of Vesuvius and its Neighbourhood.
Brit. Ass. Reports, 1889, pp. 12. with 5 woodcuts.
75 1890. The State of the Active Sicilian Volcanoes in Septem-
ber 1889. Scottish Geograph. Mag., Vol. VI, N.3, March
1890, pp. 145-150.
76 1890. Osservazioni geologichc lungo il tracciato del Grande
Emissario Fognonc di Napoli dalla Pictra sino a Pozzuo-
li. Rclazione alia Soclcta Napoletana degli Ingegneri
Costruttori di Napoli. Boll. R. Com. Geol., Vol. XXI,
N. 1 e 2., pp. 18-27 with 1 woodcut.
77 1890. Osservazioni geologichc sullc isole Veiitotcnc c Santo
Stefano ( Gruppo delle Isole Ponza ). Ibid. pp. 60-64.
78 1800. Nuovc osservazioni geologiche in Napoli e suoi diu-
torni ibid. pp. 65-68. (A curious error has been made
by the translator \vho seems to have been affected by a
mental Daltonism. ( On page 67, Hue 3, 6 and 9 for
"verdi" "read rossi" i.e. for " green " read " red. ")
;<> J800. The Eruption of Vulcano Island. -- "Nature" Vol.
XLH, pp. 78-79.
.sv> 1HOO. The Extension of the Mellard Reade and C. Davison
Theory of Secular Straining of the Earth to the Expla-
nation of the Deep Phenomena of Volcanic Action. -
Oeol. Mag., Dec. Ill, I'ol. VII. June, pp. 246-249.